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WO1997012543A1 - Appareil et methode de mesure d'une perturbation induite pour determiner un parametre physiologique - Google Patents

Appareil et methode de mesure d'une perturbation induite pour determiner un parametre physiologique Download PDF

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Publication number
WO1997012543A1
WO1997012543A1 PCT/US1996/015879 US9615879W WO9712543A1 WO 1997012543 A1 WO1997012543 A1 WO 1997012543A1 US 9615879 W US9615879 W US 9615879W WO 9712543 A1 WO9712543 A1 WO 9712543A1
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WIPO (PCT)
Prior art keywords
waveform
patient
exciter
physiological parameter
relationship
Prior art date
Application number
PCT/US1996/015879
Other languages
English (en)
Inventor
Richard G. Caro
Mark H. Sher
Original Assignee
Vital Insite, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US08/561,923 external-priority patent/US5833618A/en
Application filed by Vital Insite, Inc. filed Critical Vital Insite, Inc.
Publication of WO1997012543A1 publication Critical patent/WO1997012543A1/fr

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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
    • A61B5/021—Measuring pressure in heart or blood vessels
    • A61B5/02133—Measuring pressure in heart or blood vessels by using induced vibration of the blood vessel
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
    • A61B5/021—Measuring pressure in heart or blood vessels
    • A61B5/022—Measuring pressure in heart or blood vessels by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers

Definitions

  • the present invention relates to an apparatus and method for noninvasively providing a determination of a patient's physiological parameter and other clinically important parameters.
  • Blood pressure is the force within the arterial system of an individual that ensures the flow of blood and delivery of oxygen and nutrients to the tissue.
  • Blood pressure is affected, during and after surgery, by the type of surgery and physiological factors such as the body's reaction to the surgery. Moreover, blood pressure is manipulated and controlled, dunng and after surgery, using va ⁇ ous medications. Often, these physiological factors and the given medications can result in a situation of rapidly changing blood pressure requinng immediate blood pressure measurement, and corrective action. Because of changes in the pauent's blood pressure, constant monito ⁇ ng is important.
  • the tradiuonal method of measuring blood pressure is with a stethoscope, occlusive cuff and pressure manometer. However, this technique is slow, subjective in nature, requires the intervention of a skilled clinician and does not provide timely readings frequently required in c ⁇ tical situations.
  • noninvasive, intermittent methods that use an automated cuff device such as an oscillomet ⁇ c cuff
  • invasive, continuous (beat-to-beat) measurements that use a catheter.
  • the oscillomet ⁇ c cuff method typically requires 15 to 45 seconds to obtain a measurement, and should allow sufficient Ume for venous recovery. Thus, at best there is typically 1/2 to 1 minute between updated pressure measurements. This is an inordinately long amount of time to wait for an updated pressure reading when fast acting medications are administered. Also, too frequent cuff inflations over extended pe ⁇ ods may result in ecchymosis and/or nerve damage in the area underlying the cuff.
  • the invasive method has inherent disadvantages including nsk of embohzation, infection, bleeding and vessel wall damage.
  • Tolles employs two sensors to detect a perturbation waveform and generate two sensor signals. The two sensor signals are compared in a phase detector. The phase difference of the sensor signals is displayed giving a signal that is capable of detecting changes in blood pressure, but which does not provide a calibrated blood pressure output.
  • Salisbury similarly employs a sensor to detect a perturbation waveform and generate a single sensor signal. The sensor signal is compared against a reference signal. Based on the phase difference of the sensor signal, a universal formula is employed to determine the patient's blood pressure.
  • the present invention describes an apparatus and method for measuring the induced perturbation of a patient's body tissue to determine the patient's blood pressure and other clinically important parameters.
  • An object of the present invention is to continuously determine a patient's blood pressure via a noninvasive sensor attached to the patient.
  • a related object is to induce a perturbation into a patient's blood or blood vessel and to noninvasively measure the perturbation to determine the patient's blood pressure.
  • a related object is to filter the noninvasive sensor signal into components including a natural component, an induced component and a noise component, and to determine the patient's blood pressure from the induced component.
  • a further related object is to determine a relationship between a property of an induced perturbation and a property of a physiological parameter.
  • a monitor for determining a patient's physiological parameter includes a calibration device configured to provide a calibration signal representative of the patient's physiological parameter.
  • An exciter is positioned over a blood vessel of the patient for inducing a transmitted exciter waveform into the patient.
  • a noninvasive sensor is positioned over the blood vessel, where the noninvasive sensor is configured to sense a hemoparameter and to generate a noninvasive sensor signal representative of the hemoparameter containing a component of a physiological parameter waveform and a component of a received exciter waveform.
  • a hemoparameter is defined as any physiological parameter related to vessel blood such as pressure, flow, volume, velocity, blood vessel wall motion, blood vessel wall position and other related parameters.
  • a processor is configured to determine a relationship between a property of the received exciter waveform and a property of the physiological parameter.
  • the processor is connected to receive the calibration signal and the noninvasive sensor signal, and the processor is configured to process the calibration signal and the noninvasive sensor signal to determine the physiological parameter.
  • the physiological parameter measured is blood pressure, however, the present invention can also be used to analyze and track other physiological parameters such as vascular wall compliance, strength of ventricular contractions, vascular resistance, fluid volume, cardiac output, myocardial contractility and other related parameters.
  • Figure 1 depicts the present invention attached to a patient
  • Figure 2 depicts an exciter attached to a patient
  • Figure 3 depicts a noninvasive sensor attached to a patient
  • Figure 4a depicts a blood pressure waveform
  • Figure 4b depicts a blood pressure waveform with an exciter waveform superimposed thereon
  • Figure 5 depicts a schematic diagram of the present invention
  • Figures 6a-b depict a processing flow chart according to one embodiment of the invention
  • FIGS. 7a-c are graphical illustrations of the filter procedures of the present invention.
  • Figures 8a-c are graphical illustrations showing the relationships between the exciter waveform and blood pressure;
  • Figures 9a-b depict a processing flow chart according to another embodiment of the invention.
  • FIGS. lOa-b depict a processing flow chart according to another embodiment of the invention.
  • Figure 11 depicts an exciter and noninvasive sensor attached to a patient.
  • V c exciter sensor signal (transmitted exciter waveform)
  • a preferred embodiment concentrates on the physiological parameter of blood pressure, however, many additional physiological parameters can be measured with the present invention including vascular wall compliance, ventricular contractions, vascular resistance, fluid volume, cardiac output, myocardial contractility and other related parameters.
  • vascular wall compliance vascular wall compliance
  • ventricular contractions vascular resistance
  • fluid volume vascular volume
  • cardiac output cardiac output
  • myocardial contractility other related parameters.
  • vanous changes and modifications can be made to the preferred embodiment while remaining within the scope of the present invention.
  • the term continuous means that the physiological parameter of interest is determined over a pe ⁇ od of time, such as dunng the course of surgery.
  • the implementation of portions of the invention in a digital computer is performed by sampling va ⁇ ous input signals and performing the descnbed procedures on a set of samples.
  • a pe ⁇ odic determination of the physiological parameter of interest is within the definition of the term continuous.
  • FIG. 1 illustrates the components and configuration of the preferred embodiment.
  • Oscillomet ⁇ c cuff 110 is connected to processor 100 via wire 106, and cuff 110 is responsive to processor 100 dunng an initial calibration step.
  • Oscillomet ⁇ c cuff operation which is known in the art, involves an automated procedure for obtaining a blood pressure signal. The general procedure is given for clarity but is not crucial to the invention. First, an occlusive cuff is pressurized around the patient's upper arm to abate the blood flow. Then, as the pressure is slowly reduced, a transducer senses when the blood flow begins and this pressure is recorded as the systolic pressure.
  • the transducer similarly detects the pressure when full blood flow is restored and this pressure is recorded as the diastolic pressure.
  • the signals representing pressure are delivered, via wire 106, to processor 100 for storage.
  • An alternative blood pressure measurement technique such as manual or automated sphygmomanometry using Korotkoff sounds or "return to flow" techniques, could also be used.
  • a manual measurement can be provided, for example, using a keypad.
  • a calibration device provides a calibration signal representative of the patient's physiological parameter.
  • the calibration device is broadly defined to include automated or manual measurements.
  • Figure 1 shows an exciter 202 attached to the patient's forearm above the radial artery.
  • the exciter 202 is a device for inducing a perturbation of the patient's body tissue, and is controlled by the processor 100 via tube 107.
  • FIG. 2 shows a cross section of the exciter and its components.
  • the exciter 202 is an inflatable bag attached to the processor via air tube 107. It is fixed in place near an accessible artery 220 by holddown device 204 which can be a buckle, adhesive strap or other device.
  • holddown device 204 which can be a buckle, adhesive strap or other device.
  • an exciter sensor 203 disposed within the exciter to generate a reference signal indicative of the perturbation source waveform, and to deliver the signal to the processor via wire 108. This signal is used as a reference signal by the processor (explained below).
  • processor 100 is attached to the exciter via tube 107.
  • the processor 100 controls the pressure in exciter 202 with a transducer and diaphragm.
  • a transducer is a device that transforms an electrical signal to physical movement
  • a diaphragm is a flexible material attached to the transducer for amplifying the movement.
  • An example of this combination is a loudspeaker.
  • the diaphragm forms part of an airtight enclosure connected to air tube 107 and an input to initialize the pressure.
  • the transducer and air tube 107 and exciter 202 can be miniaturized and combined into a single exciter element capable of acting as a vibrating air filled bag connected to the processor by an electrical drive signal alone, in the case that a source of substantially constant pressure such as a spring is included in the exciter, or by an electrical drive signal and connection to a source of substantially constant pressure for the bag.
  • the pressure is initially established via the initialization input and then the pressure is va ⁇ ed by an electrical signal delivered to the transducer; the diaphragm produces pressure variations in the tube in response to the transducer movement.
  • the processor by delivering an oscillating electncal signal to the transducer, causes oscillating exciter pressure.
  • the exciter responds by perturbing the patient's tissue and inducing a transmitted exciter waveform into the patient.
  • the perturbation excites the tissue 221 and blood vessel 220 below the exciter and causes the transmitted exciter waveform to radiate within the patient's body, at least a portion of which travels along the blood filled vessel.
  • the excitation waveform can be sinusoidal, square, triangular, or of any suitable shape. Expe ⁇ ments conducted to determine a range of satisfactory perturbation frequencies found that the range of 20-1000Hz works well. It is anticipated that frequencies of lesser than 20Hz and greater than 1000Hz will also work well, and it is intended that this specification cover all frequencies insofar as the present invention is novel.
  • Figure 1 further shows a noninvasive sensor 210 placed at a distance from the exciter on the patient's wnst.
  • the noninvasive sensor is connected to the processor 100 via wire 109.
  • Figure 3 shows a cut-away view of the noninvasive sensor 210 placed over the same radial artery 220 as the exciter.
  • the sensor 210 is fixed in place near the artery 220 by holddown device 211 which can be a buckle, adhesive strap or other device.
  • the holddown device 211 also includes a baffle 212 to reduce noise, where the baffle is a pneumatic bag pressunzed to hold the sensor 210 at a constant pressure against the patient, for example at a pressure of 10mm Hg.
  • baffle 212 can be any suitable device such as a spring or foam pad.
  • the noninvasive sensor 210 is responsive to at least one hemoparameter of the patient and generates a signal in response thereto.
  • a hemoparameter is defined as any physiological parameter related to vessel blood such as pressure, flow, volume, velocity, blood vessel wall motion, blood vessel wall position and other related parameters.
  • a piezoelectnc sensor is used to sense arterial wall displacement, which is directly influenced by blood pressure. As is shown, the sensor is positioned over the radial artery 220 and it is responsive to pressure va ⁇ ations therein: as the pressure increases, the piezoelectnc matenal deforms and generates a signal conespondmg to the deformation. The signal is delivered to the processor 100 via wire 109.
  • Figure 1 also shows the processor 100 that has a control panel for communicating information with the user.
  • a power switch 101 is for turning the unit on.
  • a waveform output monitor 102 displays the continuous blood pressure waveform for medical personnel to see. This waveform is scaled to the pressures determined by the processor, and output to the monitor.
  • a digital display 103 informs the user of the current blood pressure; there is a systolic over diastolic and mean pressure shown.
  • a calibrate button 104 permits the user to calibrate the processor at any time, by pressing the button.
  • the calibration display 105 shows the user the blood pressure at the most recent calibration, and also the elapsed time since calibration.
  • the processor maintains a record of all transactions that occur during patient monito ⁇ ng including calibration blood pressure, calibration times, continuous blood pressure and other parameters, and it is anticipated that additional information can be stored by the processor and displayed on the control panel.
  • the noninvasive sensor signal in addition to a natural hemoparameter, contains a component indicative of the exciter waveform traveling through the patient.
  • the exciter component is designed to be small in compa ⁇ son to the natural hemoparameter, it contains valuable information. Therefore, the processor is used to separate the exciter waveform from the natural hemoparameter, and to quantify the respective components to determine the patient's blood pressure.
  • Figure 4a shows a natural blood pressure waveform where the minimum represents the diastolic pressure and the maximum represents the systolic pressure.
  • This waveform has a mean arte ⁇ al pressure (MAP) that is a convenient reference for purposes of determining the DC offset of the waveform.
  • Example pressure values are 80mm Hg diastolic and 120mm Hg systolic respectively with a MAP DC offset of 90mm Hg.
  • Figure 4b shows an operational illustration of the arterial waveform; an exciter waveform superimposed on a natural blood pressure waveform.
  • the exciter induces the exciter waveform into the artenal blood at a first location and the exciter waveform becomes superimposed on the natural waveform. Since the exciter waveform is small compared to the patient's natural waveform, the natural waveform dominates as shown in Figure 4b.
  • the noninvasive sensor signal contains information regarding both the natural waveform and the exciter waveform.
  • the processor 100 is designed to separate the constituent components of the noninvasive sensor signal to continuously determine the patient's blood pressure, as is discussed below.
  • Figure 5 depicts a schematic diagram of the prefened embodiment.
  • an oscillometric cuff controller 121 for controlling the oscillometric cuff and determining the readings therefrom to generate a signal representing the patient's blood pressure.
  • the transducer output is connected to the exciter 202 and controls the exciter's oscillations for inducing the exciter waveform into the patient's arterial blood.
  • the output of the exciter sensor 203 is fed to a band pass filter 134.
  • This filter 134 separates the high frequency signal responsive to the transducer pressure and delivers the resulting signal to RMS meter 135 and to lock-in amplifier 143 reference input.
  • the RMS meter output is sampled at a rate of 200 samples per second with a 14 bit resolution and delivered to computer 150. It is anticipated that the sampling rate and resolution can be varied with good results.
  • the output of the noninvasive sensor is fed to a charge amplifier 140 that delivers a resulting signal to a low pass filter 141 and a band pass filter 142.
  • These filters separate the noninvasive sensor signal into two constituent components representing an uncalibrated natural blood pressure wave and a received exciter waveform respectively.
  • the low pass filter output is sampled at a rate of 200 samples per second with 14 bit resolution and delivered to computer 150, and the band pass filter output is delivered to the lock-in amplifier 143 signal input.
  • the lock-in amplifier 143 receives inputs from band pass filter 134 as reference and band pass filter 142 as signal, which are the exciter sensor signal (transmitted exciter waveform) and noninvasive sensor exciter signal (received exciter waveform) respectively.
  • the lock-in amplifier uses a technique known as phase sensitive detection to single out the component of the noninvasive sensor exciter signal at a specific reference frequency and phase, which is that of the exciter sensor signal.
  • the amplifier 143 produces an internal, constant-amplitude sine wave that is the same frequency as the reference input and locked in phase with the reference input. This sine wave is then multiplied by the noninvasive sensor exciter signal and low-pass filtered to yield a signal proportional to the amplitude of the noninvasive sensor signal multiplied by the cosine of the phase difference between the noninvasive exciter signal and the reference. This is known as the in-phase or real output.
  • the amplifier 143 also produces an internal reference sine wave that is 90 degrees out-of-phase with the reference input. This sine wave is multiplied by the received exciter signal and low-pass filtered to yield a signal proportional to the amplitude of the noninvasive sensor signal multiplied by the sine of the phase difference between the noninvasive sensor exciter signal and the reference. This is known as quadrature or imaginary output.
  • the amplifier 143 then provides the computer 150 with information regarding the real and imaginary components of the received exciter signal as referenced to the phase of the transmitted exciter signal. Alternately, the amplifier can provide components representing the magnitude and phase of the received exciter signal. In the preferred embodiment, the amplifier output is sampled at a rate of 200 samples per second with a 14 bit resolution. It is anticipated that the sampling rate and resolution can be varied with good results.
  • the computer 150 receives input from the oscillometric cuff controller 121,
  • the computer 150 also receives input from the user interface panel 160 and is responsible for updating control panel display information.
  • the computer 150 executes procedures for further separating constituent components from the noninvasive sensor signal and attenuating the noninvasive sensor noise component as shown in Figure 6.
  • PROCESS EXCITER WAVEFORM VELOCITY TO DETERMINE OFFSET SCALING AND EXCITER WAVEFORM AMPLITUDE TO DETERMINE GAIN SCALING Figure 6 is a processing flowchart that represents the operation of the
  • Step 702 The operation begins at step 702 with the receipt of an initial calibration measurement; noninvasive sensor signal and exciter sensor signal.
  • Step 704 chooses the blood pressure waveform segment for pulse reference, which is important for continuity of measurement from pulse to pulse and for consistency over periods of time between calibration measurements.
  • the diastolic pressure low-point
  • any point of the waveform can be chosen such as the systolic pressure or mean arterial pressure (MAP).
  • MAP mean arterial pressure
  • Step 706 is a filter step where the noninvasive sensor (received) exciter waveform is separated into signal and noise components.
  • the noise components may have many sources, one of which is a signal derived from the exciter that travels to the noninvasive sensor by an alternate path, other than that along the artery taken by the signal of interest.
  • sources include bones conducting the exciter waveform and the surface tissue such as the skin conducting the exciter waveform. Additional sources of noise result from patient movement. Examples include voluntary patient motion as well as involuntary motion such as movement of the patient's limbs by a physician during surgery.
  • Figures 7a-c illustrate the principles of the received exciter signal filtering.
  • the received exciter waveform V d is represented by a collection of points that are generated in the complex plane by the real and imaginary outputs of the lock-in amplifier 143 which is monitoring the noninvasive sensor signal.
  • Figure 7a represents the received exciter waveform V d in the absence of noise.
  • V d is the same as vector V w (t) which has a magnitude and phase conesponding to the received exciter signal.
  • the magnitude of V w (t) remains constant, but the angle periodically oscillates from a first angle representing a lesser pressure to a second angle representing a greater pressure. Note that in the absence of noise, the arc has a center at the origin.
  • Figure 7b represents the received exciter waveform V d in the presence of noise, which is indicated by vector V n .
  • Vector V d has a magnitude and phase according to the noninvasive sensor exciter waveform plus noise.
  • vector V d (t) defines a collection of points forming an arc having a common point V c equidistant from each of the collection of points.
  • the vector V n represents noise and, once identified, can be removed from the noninvasive sensor waveform.
  • the filter step removes the V n noise component and passes the V w (t) signal exciter component on to step 708.
  • step 706 involves the arrangement of data from one or more cardiac cycles in the complex plane depicted in figure 7a-c.
  • a circle is fit to this data in the complex plane using a fitting technique such as the minimization of least-square enor between the data and the fitted circle.
  • the radius and center location of the fitted circle are the adjustable parameters in this process.
  • V w (t) the magnitude of V w (t) remains constant over the time of a pulse.
  • the attenuation of the exciter waveform as it propagates along the artery is pressure dependent, and in those cases the magnitude of V w (t) can vary during the pulse in a way that is conelated to pressure.
  • V d the shape of the figure traced out in the complex plane by the vector V d will deviate from a perfect circle segment.
  • a typical shape is that of a spiral with a form that can be predicted theoretically.
  • the functioning of this filter step under such circumstances is conceptually similar to that described above, except that the elimination of the noise vector V n must involve location of the origin of a spiral rather than of the center of a circle.
  • Step 708 determines if the pulse is valid.
  • the processor checks the constituent components of the noninvasive sensor signal to insure that the components are within acceptable clinical norms of the patient. For example, the processor can determine whether the new pulse is similar to the prior pulse, and if so, the new pulse is valid.
  • Step 720 processes the signal exciter waveform V w (t) to determine the DC offset.
  • the diastole is used as the offset value, but any part of the waveform can be used.
  • the processor determines the offset when the vector V w (t) reaches its lowest phase angle (i.e., the maximum clockwise angle of Figure 7a); this is the diastole phase angle ⁇ w(dias).
  • a calibration diastolic measurement is stored by the processor at calibration as Pro. Also stored by the processor is a relationship denoting the relationship between the velocity of an exciter wave and blood pressure. This relationship is determined by reference to a sample of patients and is continuously updated by reference to the particular patient after each calibration measurement.
  • Figure 8a-c are graphical illustrations showing clinically determined relationships between the exciter waveform and blood pressure.
  • Figure 8b represents the relationship between phase and pressure at a frequency of 150Hz; other frequencies have relationships that are vertically offset from the line shown.
  • the pressure-velocity relationship represents the storage of this graphical information either in a data table or by an analytical equation.
  • Step 721 determines the predicted diastolic pressure from the information in Step 720.
  • the processor continuously determines the change in diastole from one pulse to the next by referencing the position of the signal exciter vector V w (t), at ⁇ w(dias), with respect to the stored pressure- velocity relationship.
  • the pressure-velocity relationship is continuously updated based on calibration measurement information gained from past calibrations of the patient.
  • a set of established relationships is used to develop and interpret information in the table and to relate the information to the sensor signal components. First, a known relationship exists between blood pressure and exciter waveform velocity.
  • the new DC offset diastolic pressure is predicted P D (pred). This prediction is made based on the diastolic pressure at calibration P D0 plus the quotient of the phase difference between calibration ⁇ w D0 and the present time ⁇ w(dias) and the pressure-velocity relationship stored in processor memory as rate of change of exciter waveform phase to pressure d( ⁇ w D )/dP.
  • Step 722 displays the predicted diastolic pressure.
  • Step 730 determines the noninvasive sensor exciter waveform phase and velocity. This determination is made based on the comparison of the noninvasive sensor exciter waveform with the exciter sensor waveform.
  • Step 731 determines the noninvasive sensor exciter waveform amplitude from the noninvasive sensor signal.
  • Step 732 determines the exciter waveform pressure P w by multiplying the exciter sensor waveform magnitude V c by the ratio of the calibrated exciter waveform pressure P w (cal) to the calibrated exciter sensor waveform magnitude V.(cal). ' VJieati
  • Step 734 determines if the calibration values are still valid. This determination can be based on many factors including the time since the last calibration, that the linearity of the pressure- velocity relationship is outside of a reliable range, determination by medical personnel that a new calibration is desired or other factors. As an example of these factors, the prefened embodiment provides user settable calibration times of 2, 5, 15, 30, 60 and 120 minutes, and could easily provide more. Moreover, the curve upon which the pressure is determined is piecewise linear with some degree of overall nonhnearity. If the processor 100 determines that the data is unreliable because the linear region is exceeded, the processor will initiate a calibration step. Finally, if the operator desires a calibration step, a button 104 is provided on the processor 100 for initiating calibration manually.
  • Step 736 predicts a new pulse pressure P p (pred) by multiplying the exciter waveform pressure P w by the ratio of the detected pulsatile voltage V p to the detected exciter waveform magnitude V w .
  • This prediction uses the noninvasive sensor exciter waveform to determine the pressure difference between the diastole and systole of the natural blood pressure waveform. For example, if a noninvasive sensor exciter magnitude V w of 0.3V relates to a pressure variation P w of 1mm Hg and the noninvasive sensor waveform V p varies from -6V to +6V, then the noninvasive sensor waveform represents a pulse pressure excursion P p (pred) of 40mm Hg.
  • Step 760 predicts a new systolic pressure P s (pred) by adding the predicted diastolic P D (pred) and pulse pressures P p (pred).
  • the new systolic P,(pred) is 120mm Hg. Then the new systolic pressure is displayed.
  • the values determined for P s (pred) and P D (pred) can be displayed numerically.
  • the output waveform for display 102 can be displayed by scaling the noninvasive sensor natural blood pressure waveform prior to ou ⁇ ut using gain and offset scaling factors so that the output waveform has amplitude, P P (pred), and DC offset, P D (pred), equal to those predicted in the above process.
  • the scaled output waveform signal can also be ou ⁇ ut to other instruments such as monitors, computers, processors and displays to be used for display, analysis or computational input.
  • Step 750 is taken when step 734 determines that the prior calibration is no longer reliable as described above.
  • a calibration step activates the oscillometric cuff 201 and determines the patient's blood pressure, as described above.
  • the processor 100 uses the calibration measurements to store updated pressure and waveform information relating to the DC offset, blood pressure waveform and exciter waveform.
  • the updated variables include calibration pulse pressure P p (cal), calibration exciter sensor waveform magnitude V e (cal), diastolic pressure Poo, diastolic exciter waveform phase W D Q, the rate of change of exciter waveform phase to pressure d( ⁇ w D )/dP and calibration exciter waveform pressure P w (cal).
  • FIGS 9a-b represent a modification to the previous embodiment.
  • the initial processing steps 702, 704, 706, 708, 730 and 731 represented in the flow chart of Figure 9 are substantially similar to those described in the previous embodiment depicted in Figure 6.
  • step 730 exciter waveform velocity Vel(t) and the actual phase delay of the exciter waveform ⁇ (t) are related by the equation:
  • ⁇ (t) ⁇ 0 - 2 ⁇ df/Vel(t) (6)
  • n is an integer also known as the cycle-number, typically in the range of 0- 10. While conect deduction of propagation velocity requires a conect choice of n, a conect prediction of pressure using a pressure-velocity relation does not, so long as the same value of n is used in determining ⁇ (t) and in determining the pressure- velocity relationship. In such a case, velocity should be considered as a pseudo- velocity rather than an actual measure of exciter waveform propagation speed.
  • step 730 therefore, use of the ⁇ (t) equations allows determination of the velocity, or pseudo-velocity, Vel(t) as a function of time.
  • step 801 the values of velocity at the systolic and diastolic points of the cardiac cycle are determined as Vel s and Vel D . These conespond to the points of minimum and maximum phase delay or to the points of maximum and minimum amplitude of the naturally occurring blood pressure wave detected by the noninvasive sensor.
  • Use of the pressure-velocity relationship stored in the processor is then made to transform the values of velocity at systolic and diastolic points in time to values of pressure.
  • step 803 the diastolic pressure is determined using the equation:
  • Step 804 is performed to determine the predicted systolic pressure according to the relationship:
  • step 805 the calculated pressures are displayed as numbers, with a typical display comprising display of mean, systolic and diastolic values of the pressure waveform in digital form, together with the observed pulse rate.
  • the values of P D (pred) and P s (pred) are used to determine appropriate gain and DC offset scaling parameters by which the naturally occurring blood pressure waveform detected by the noninvasive sensor is scaled prior to ou ⁇ ut in step 806 as a time varying waveform, shown as 102 in Figure 1.
  • step 750 involves a calibration step initiated when step 734 determines that the prior calibration is no longer reliable.
  • the pressure-velocity relationship is determined and stored in the processor in the form of a table or of an analytical relationship.
  • values of gain Pp(pred) and offset P D (pred) are determined and used to scale the noninvasive sensor natural blood pressure waveform to provide a time varying output waveform representative of the patient's blood pressure.
  • the natural blood pressure waveform monitored by the noninvasive sensor is not used in the determination of the output blood pressure waveform
  • exciter waveform velocity is measured many times dunng a cardiac cycle (typically 50 - 200 times per second) and the resultant determinations of pressure are used to construct the output time varying blood pressure waveform. This process is descnbed below with reference to Figure 10.
  • the natural blood pressure waveform is not scaled. Therefore, there is no need to separate the data into pulse segments as in step 704 of Figure 6.
  • This feature greatly simplifies the computational task.
  • An additional advantage of this technique is that all of the information used in the analysis process is encoded in the exciter waveform, which is typically at a high frequency compared with that of both the natural blood pressure waveform and that of any artifact signals introduced by patient motion or respiration. Since all of these lower frequency signals can be removed by electronic filtenng, this technique is extremely immune to motion induced artifact and similar sources of interference that might otherwise introduce enors into the measurement.
  • the initial processing steps 702,706, 731 and 730 are substantially similar to those of previously descnbed embodiments.
  • the amplitude and phase of the exciter waveform determined in step 731 are continuous functions of time.
  • the exciter waveform phase is converted to exciter waveform velocity as descnbed previously, which is also a continuous function of time.
  • the time dependent velocity function Vel(t) is readily transformed to a time dependent pressure function P(t). This transformation is represented by step 802.
  • the pressure-velocity relationship might be as follows-
  • Vel(t) a + bP(t) (10) where the constants a and b were determined during step 750. In that case the velocity equation (10) can be used to perform the transformation of step 802.
  • step 806 the entire time dependent waveform is displayed as waveform 102.
  • an important step involves the conversion of a measured phase to a deduced exciter waveform velocity, and conversion of that value to a pressure.
  • this process is integral to the calculation of the DC offset pressure P m .
  • this process is integral to determination of P s and P D .
  • the process is integral to the determination of pressure at each point in time for which an ou ⁇ ut value is to be displayed as part of a "continuous" pressure waveform display.
  • step 750 in each of the embodiments described in Figures 6, 9, and 10, and the relationship is stored in the processor in either a tabular form, or as an analytical relationship.
  • step 734 in Figures 6, 9 and 10 a variety of parameters are examined to determine whether the system calibration continues to be acceptable. As part of that process, it is determined whether the existing pressure- velocity relationship continues to be valid. If not, a recalibration can be initiated.
  • an additional embodiment is described using multiple perturbation waveforms. All the features and advantages of the prior embodiments are applicable to these embodiments.
  • an embodiment is described in which the apparatus further induces a second exciter waveform into the arterial blood.
  • An example second exciter waveform is one that has a frequency different from that of the first exciter waveform. It is noted that although the discussion of the second embodiment concentrates on a second exciter wave, any number of two or more exciter waves can be used to determine the perturbation velocity measurement.
  • processor 100 In operation, processor 100 generates two exciter waveforms and communicates the waveforms to the exciter 202 via air tube 107.
  • the exciter 202 responds by inducing both exciter waveforms into the patient.
  • Noninvasive sensor 210 generates a signal responsive to a hemoparameter and transmits the signal to the processor 100 via wire 109.
  • the processor filters the noninvasive sensor signal into components of the natural waveform, a first exciter waveform, a second exciter waveform and noise.
  • the processor determines the phase relationship of the first exciter waveform to a first reference input and determined the phase relationship of the second exciter waveform to a second reference input.
  • the processor then generates a plurality of points, the slope of which relates to the velocity of the exciter waveform. This is shown in Figure 8c, where the slope of the line is -2 ⁇ d/Vel, and where d is distance and Vel is velocity. Since the distance is fixed and the slope is related to blood pressure, and since the slope changes based on changes in blood pressure, the velocity of the exciter waveform is determined. The technique described above yields a measurement of the group velocity.
  • phase velocity or of a pseudo-phase velocity in the case that the value of n of the phase equation (7) can not be uniquely determined.
  • these values need not always agree.
  • phase, group and pseudo-velocity are monotonically varying functions of pressure.
  • a measurement of any one of the three is a basis for a pressure prediction, so long as the appropriate pressure- velocity relationship is used.
  • An additional benefit of the use of multiple frequency perturbations is that it allows the unique determination of the value of n in the phase measurement equation descnbed above. This allows the use of actual phase velocity, rather than of the pseudo-velocity descnbed earlier in the multi-perturbation analogues of the embodiments depicted in Figures 6, 9 and 10.
  • FIG. 11 Another embodiment is depicted in Figure 11 showing a cross section of an exciter 202 and noninvasive sensor 210 at the same position above the blood vessel 220.
  • the proximate location of the exciter and the sensor permits measurement of the blood vessel's response to the perturbations.
  • the noninvasive sensor is responsive to a hemoparameter such as blood flow or blood volume. These parameters can be measured with a sensor such as a photoplethysmograph. Detected changes in the blood vessel due to the natural pulsatile pressure are calibrated using external exciter pressure oscillations and compared against the sensor signal by the processor.
  • Additional embodiments include an embodiment in which two or more detectors are positioned along the artery at different distances from a single exciter, and an embodiment in which two or more exciters are positioned along the artery at different distances from one or more detectors.
  • the information obtained from each exciter detector pair can be analyzed independently.
  • the multiply redundant measurements of pressure that result can be combined to provide a single pressure determination that may be both more accurate and more immune from noise, motion artifact and other potential enor sources. Similar redundancy can be achieved in the embodiments that use multiple exciter waveforms by analyzing the results at each frequency independently and combining the results to provide enhanced robustness.
  • any combination of more than two elements allows the value of n in the phase equation (7) to be uniquely determined so long as the spacing of two of the elements is sufficiently small to be less than a wavelength of the propagating perturbation. Since the possible range of perturbation wavelengths at a given pressure can be determined from a pool of patients, selection of the appropriate spacing is straightforward and can be inco ⁇ orated into the geometrical design of the device.
  • a close relationship between physiological parameters and hemoparameters supplies valuable information used in the present invention.
  • the perturbation of body tissue and sensing the perturbation also supplies valuable information used in the present invention.
  • the prefened embodiment concentrates on blood pressure
  • the present invention can also be used to analyze and track other physiological parameters such as vascular wall compliance, changes in the strength of ventricular contractions, changes in vascular resistance, changes in fluid volume, changes in cardiac output, myocardial contractility and other related parameters.
  • Calibration signals for the present invention can be obtained from a variety of sources including a catheter, manual determination, or other similar method.
  • the DC offset for the physiological parameter waveform can be obtained in a variety of ways for use with the present invention.
  • the exciter of the prefened embodiment uses air, but any suitable fluid can be used.
  • various exciter techniques can be used for inducing an exciter waveform into the patient such as an acoustic exciter, an electromagnetic exciter and an electromechanical exciter (e.g. piezoelectric device).
  • Noninvasive sensors have been developed for sensing hemoparameters. These sensor types include piezoelectric, piezoresistive, impedance plethysmograph, photoplethysmograph, various types of strain gages, air cuffs, tonometry, conductivity, resistivity and other devices.
  • the present invention can use any sensor that provides a waveform related to the hemoparameter of interest.

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  • Health & Medical Sciences (AREA)
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  • Cardiology (AREA)
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  • Heart & Thoracic Surgery (AREA)
  • Medical Informatics (AREA)
  • Biophysics (AREA)
  • Pathology (AREA)
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  • Measuring Pulse, Heart Rate, Blood Pressure Or Blood Flow (AREA)

Abstract

L'invention concerne un dispositif de détection servant à déterminer un paramètre physiologique du patient, qui comprend un appareil d'étalonnage (110) configuré de manière à produire un signal de mesure représentatif du paramètre physiologique en question. Un stimulateur (202) est placé sur un vaisseau sanguin du patient afin de transmettre une forme d'onde à celui-ci. Un capteur (210) en surface placé sur le vaisseau sanguin capte un hémoparamètre et génère un signal représentatif de cet hémoparamètre, qui contient une composante de la forme d'onde reçue du stimulateur. En l'espèce, il faut entendre par hémoparamètre tout paramètre relatif au sang, comme par exemple la pression, le flux, le volume, la vitesse, la mobilité des parois des vaisseaux sanguins, la position de ces parois et autres paramètres apparentés. Un processeur (100) détermine une relation entre une propriété de la forme d'onde de stimulation reçue et une propriété du paramètre physiologique. Le processeur de données (100) reçoit le signal d'étalonnage et le signal du capteur en surface, afin de déterminer la paramètre physiologique. Dans le mode préférentiel de réalisation, le paramètre physiologique ainsi mesuré est la tension artérielle, mais cette invention peut également être utilisée pour analyser et suivre d'autres paramètres physiologiques tels que l'élasticité des parois vasculaires, la force des contractions ventriculaires, la résistance vasculaire, le volume du fluide, le débit cardiaque, la contractilité myocardiaque et d'autres paramètres connexes.
PCT/US1996/015879 1995-10-03 1996-10-02 Appareil et methode de mesure d'une perturbation induite pour determiner un parametre physiologique WO1997012543A1 (fr)

Applications Claiming Priority (4)

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US517995P 1995-10-03 1995-10-03
US60/005,179 1995-10-03
US08/561,923 1995-11-22
US08/561,923 US5833618A (en) 1994-04-15 1995-11-22 Apparatus and method for measuring an induced perturbation to determine a physiological parameter

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9949648B2 (en) 2003-07-07 2018-04-24 Nellcor Puritan Bennett Ireland Continuous non-invasive blood pressure measurement apparatus and methods providing automatic recalibration

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3090377A (en) * 1961-10-30 1963-05-21 Peter F Salisbury Blood pressure measurement
US3095872A (en) * 1959-11-27 1963-07-02 Cutler Hammer Inc Blood pressure measurement
US4646754A (en) * 1985-02-19 1987-03-03 Seale Joseph B Non-invasive determination of mechanical characteristics in the body
US4869261A (en) * 1987-03-27 1989-09-26 University J.E. Purkyne V Brne Automatic noninvasive blood pressure monitor
US5279303A (en) * 1991-06-14 1994-01-18 Colin Electronics Co., Ltd. Blood pressure monitor system

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3095872A (en) * 1959-11-27 1963-07-02 Cutler Hammer Inc Blood pressure measurement
US3090377A (en) * 1961-10-30 1963-05-21 Peter F Salisbury Blood pressure measurement
US4646754A (en) * 1985-02-19 1987-03-03 Seale Joseph B Non-invasive determination of mechanical characteristics in the body
US4869261A (en) * 1987-03-27 1989-09-26 University J.E. Purkyne V Brne Automatic noninvasive blood pressure monitor
US5279303A (en) * 1991-06-14 1994-01-18 Colin Electronics Co., Ltd. Blood pressure monitor system

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9949648B2 (en) 2003-07-07 2018-04-24 Nellcor Puritan Bennett Ireland Continuous non-invasive blood pressure measurement apparatus and methods providing automatic recalibration

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